Sporangium

sporangium [ spuh-RAN-jee-uhm ] noun, plural sporangia: a sac or receptacle in which reproductive spores are produced and stored

The sporangia of native Adiantum pedatum (maidenhair fern) appear in narrow bands on the underside of the pinnules near the lobed tips, which fold over partially covering the sori. — The sporangia of native *Adiantum pedatum* (maidenhair fern) appear in narrow bands on the underside of the pinnules near the lobed tips, which fold over partially covering the sori. Image © Mary Free

Although sporangia, in which spores are produced and stored, are often associated with fungi and seedless plants, such as bryophytes (e.g., mosses) and ferns, they occur in all plants sometime during their life cycles.

Mosses have a single sporangium at the terminus of a long stalk. In ferns, sporangia appear in clusters called sori, located on the undersides of some fronds or in bead-like aggregates, sometimes on separate fertile fronds. The leaves that bear the sporangia are called sporophylls.

Each moss sporophyte consists of a sporangium atop a seta.
Photo © Mary Free

The sori consisting of stalked sporangia of native Dryopteris marginalis appear on either side of the median vein of a pinnule in-between the margin and the midrib. — Stalked sporangia of native *Dryopteris marginalis* (marginal wood fern) appear on either side of the median vein of a pinnule in-between the margin and the midrib. Photo © Elaine Millls

Bead-like sporangia of a fertile frond of native Osmundastrum cinnamomeum. — Bead-like sporangia of a fertile frond of native *Osmundastrum cinnamomeum* (cinnamon fern) in April.
Photo © Elaine Mills

Bead-like, sori-containing capsules sit atop the sterile, egg-shaped leaflets of Osmunda spectabilis — Bead-like, sori-containing capsules
of native *Osmunda spectabilis* (royal fern) in May.
Photo © Mary Free

Sori of native Polystichum acrostichoides are arranged in tightly packed rows on the undersides of pinnae. — Sori of native *Polystichum acrostichoides* (Christmas fern) are arranged in tightly packed rows on the undersides of pinnae.
Photo © Mary Free

Comparable structures in conifers are located on the strobili. In the male stobilus or microstrobilus, the sporophylls are called micosporophylls and the sporangia, microsporangia, which produce the pollen. In most microstrobili, the microsporangia are located on the abaxial (under) side of the micosporophylls. In Taxaceae (yew) the microsporangia surround a central stalk. (Schulz, et. al. 2014) The number of microsporangia per micosporophyll differs among species and even within a species. In Pinus (pine), there are two micosporangia per micosporophyll. In the female strobilus or megastrobilus of pine, two megasporangia, which develop into seeds, appear on the adaxial (upper) surface of the megasporophyll (scale-like structure) of the seed cone.

Liquid-preserved pollen cone of Ephedra sp. showing exserted microsporangia. Photo by Curtis Clark CC BY-SA 2.5 — Liquid-preserved pollen cone of *Ephedra* sp. showing exserted microsporangia. Photo by Curtis Clark CC BY-SA 2.5

A fluorescence micrograph of pollen grains in the microsporangia of an anther of Arabidopsis thaliana (thale cress). Photo by Heiti Paves CC BY-SA 3.0 — A fluorescence micrograph of pollen grains in the microsporangia of an anther of
*Arabidopsis thaliana* (thale cress). Photo by Heiti Paves CC BY-SA 3.0

Likewise, flowering plants possess microsporangia and megasporangia. The anther of the male reproductive organ or stamen usually contains four microsporangia in which pollen grains develop. Megasporangia occur inside the female ovules, which develop into seeds.

References

Carter S, Lumen Learning. Introduction to Seedless Plants. Lumen Learning. License: CC BY: Attribution. (accessed June 13, 2021).

Schulz C, Klaus K, Knopf P, Mundry M, Dörken V, Stützel T. 2014. Male Cone Evolution in Conifers: Not All That Simple. American Journal of Plant Sciences, 5: 2842-2857. doi: 10.4236/ajps.2014.518300.